Fuel Filters

[Stache]

I have been investigating an aircraft accident do to fuel exhaustion. What we found was an inline fuel filter (automotive) type installed before the fuel selector. The fuel boost pump was installed after the fuel selector. The question I have is what is the minimum filter screen in microns that should be used for aviation fuel.

Second, will aviation fuel damage automotive fuel filters (paper type).

How much pressure would it take to unload a plugged paper fuel filter.

Any help will be of assistance.

Stache

 

[WKTaylor]

Stache..

First.. it sounds like the engine failed due to fuel starvation [not enough fuel]... NOT fuel exhaustion [available/usable fuel depleted to "0"].

Suggest contacting the engine manufacturer [engineering and tech support] for fuel-type/filter recommendations...

Suggest contacting the fuel filter manufacturer [engineering and tech support] for fuel-compatibility recommendations... generally speaking gasoline-is-gasoline... but NOT always.

There are fuel filter contamination tests available thru SAE for both aircraft and auto filter elements. Contaminating a fuel filter followed by a forced-flow-test will probably answer Your question "how much pressure to unload a plugged fuel filter".

NOTE: in military acft accidents the last fueling and servicing sources [truck, underground dispersement, Hydraulic mule, etc] are immediately impounded and tested for contaminates... "just-in-case".


Regards, Wil Taylor

 

[Stache]

Will,

Thanks for the post. I have contacted the NTSB and they are going to test the filters. I took fuel samples from the source, however the fire department did not help by spraying water / foam in the fuel tanks of the aircraft.

Stache

 

[WKTaylor]

Stache..

I assume that the "source" was the refuel source such as truck, pump, etc... Not just the acft tanks.

Suggest You consider checking other aircraft serviced by "the source"... to see if any of them show signs of [the same] contaminates.

Also, consider that contaminates are sometimes introduced in previous refuelings, in routine maintenance or hidden material deterioration [such as rubber or paint flaking/cracking or metallic corrosion]

May we presume that fuel chemistry was "nominal"??

Also... are the fuel lines large enough, and routed properly, to handle max flow-rates without vapor lock or flow stagnation, IE: no tube kinks, "choke-points", engine hot-spots, adequate ID's and smooth turns, etc??? Also factor in atmospheric conditions such as high temps, freezing temps [ice formation in lines??], altitude, prolonged flight in attitude(s) adverse for smooth fuel flow/pressure... etc.

Some study of USAF T-2 [modified Firefly] mishaps [accidents] due to engine failure [fuel starvation at low altitude with loss of control] might be useful.

Also... for human factors... when engine failed, did prop windmill with a dramatic increase in drag [sudden decrease in airspeed due to wind-milling prop drag] or adverse handling characteristics [such as reduced yaw or pitch stability for a large wind-milling prop]???

PS: I can’t help "helping"... I’ve been a USAF mishap investigator way-too-long.


Regards, Wil Taylor

 

[airplanefrank]

Ahh...As a preofessional engineer and airplane builder with a passion around fuel system design this is one of my favourites.

Its not ideal to have a filter before the pump but often the desire to protect a rotovane type hi pressure fuel pump often overrides the potential issues.

You may not have so much of a plugged filter issue, more probably a small leak ahead of the filter and and the fuel pump has become air locked...I.e the pressure falls close to zero as air enters the inlet of the pump. Either that or the hi vapour pressure fuel boiled at the inlet and thus vapour locked the pump instead.

What I think you need to do is to rig the pump up and the filter and see how much the pump will flow with the current set up...Depending on the power of the engine I would expect it to run rough at around 5 gallons per hour.

Now if full power was being demanded and the mixture was set to full rich (for say a 180 Lycoming) this fuel flow would need to be close to 20GPH (US).

A big no-no is a single filter which becomes a single point of failure with no back up filter or bypass method.

AVgas is perfectly compatible with all filter elements, in fact its simply leaded fuel, no more no less.

Frank